Conventionally, a thrust balancing mechanism is used for balancing thrust force generated on a rotary shaft of a pump.
For instance, Patent Document 1 discloses a multistage centrifugal pump having a thrust balancing device including a balance sleeve inserted into a shaft portion of the pump. In this thrust balancing device, while one end face of the balance sleeve is located on the rear side of the final stage impeller, the other end of the balance sleeve is adjacent to a space communicating with a suction side of the pump. Further, a force in an opposite direction to a thrust force, which is a reverse thrust force, is transmitted to the pump shaft corresponding to the pressure difference at both end faces of the balance sleeve, that is, the difference between a discharge pressure and a suction side pressure at the final stage impeller.